Blocks Not saving after update

Hi,
I’m having a problem after yesterdays update. When I try to create a new block, it seems to work and I get the message as the “page was published” and the instructions to create the template, but when I try to open the newly created block (to edit) it is totally blank, as if nothing would have been saved to database. The block shows in the block list with the right title, but it is empty.
My site is hosted in Pantheon, and that may be important (Pantheon is not a regular LAMP server stack). I also have a local (non-pantheon) WP install, and that one seems to work fine. Also, the previous version was working fine in my Pantheon install.
Did as much troubleshooting as possible (disable/enable, uninstall/reinstall, cloned the environment and tested… same problem).
I hope you can help!! Thanks!!